White glue is NOT fuel or water proof. CA does not dissolve rapidly in fuel. If you take a lump of cured CA and put it in a sealed jar of raw fuel, it will eventually dissolve. For modeling purposes, it is fuel proof enough for almost any use. Just wipe the fuel off at the end of the day. It can be of concern when the wood gets fuel soaked at the joints. It is more a point of interest than a point of concern.

Polyurethane is used in a rather generic way in the US. It can come as a two part product, as you are refering to, or as a one part.. ready to apply product. Having never used it for your intended purpose, I will not venture a guess as to how it might work. As someone else suggested, make a mock up and try it before applying it to your model.

JR